VNX-757: TLS negotiation allows an obsolete protocol version or broken cipher suite (algorithm downgrade)

Reports TLS configuration that lets peers negotiate SSL 2/3, TLS 1.0 or TLS 1.1, or offers an RC4, DES, NULL, EXPORT or anonymous cipher suite, in Go, Java and Python.

Field	Value
Rule ID	`VNX-757`
Severity	High
SARIF level	`error`
Kind	`sast`
Languages	Go, Java, Python
CWE	CWE-757
CAPEC	CAPEC-66
ATT&CK	T1190
CWSS vector	`CWSS:1.0/TI:H/AP:A/AL:A/IC:N/FC:LT/RP:N/RL:A/AV:I/AS:N/IN:A/SC:A/BI:H/DI:H/EX:H/EC:N/P:H`
Tags	`crypto` `tls` `downgrade` `cwe-757`
Source	`internal/sast/rules/vnx-757.rego`

Overview

VNX-757 maps to CWE-757: Selection of Less-Secure Algorithm During Negotiation (‘Algorithm Downgrade’). It reports TLS settings that let a connection settle on an obsolete protocol version or a broken cipher suite: Go tls.Config MinVersion/MaxVersion set to VersionSSL30, VersionTLS10 or VersionTLS11, and RC4/3DES suites in CipherSuites; Java SSLContext.getInstance("TLSv1"), setEnabledProtocols/setEnabledCipherSuites with obsolete values, the https.protocols and jdk.tls.*.protocols properties, and a jdk.tls.disabledAlgorithms value that no longer disables SSLv3; Python ssl.PROTOCOL_TLSv1-style constants, pyOpenSSL TLSv1_METHOD, a lowered minimum_version, cleared OP_NO_* flags and set_ciphers() strings that enable RC4, DES, NULL, EXPORT, LOW or MD5.

It does not report TLS 1.2/1.3, SSLContext.getInstance("TLS"), comparisons or lookup tables of version constants, version names in log messages or comments, excluded cipher tokens (!RC4) or test files.

Why This Matters

An attacker in the network path can strip the stronger options from the handshake. If the server or client still accepts SSL 3.0 or TLS 1.0, or still offers RC4 or export suites, the connection falls back to them, and POODLE, BEAST, RC4 biases and similar attacks then apply.

What Gets Flagged

return &tls.Config{
    MinVersion: tls.VersionTLS10,                 // flagged
    CipherSuites: []uint16{
        tls.TLS_RSA_WITH_RC4_128_SHA,             // flagged
    },
}

SSLContext ctx = SSLContext.getInstance("TLSv1");                    // flagged
s.setEnabledProtocols(new String[] {"TLSv1.2", "TLSv1.1", "TLSv1"});  // flagged

ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)          # flagged
ctx.minimum_version = ssl.TLSVersion.TLSv1        # flagged
ctx.set_ciphers("ECDHE+AESGCM:RC4-SHA:!aNULL")    # flagged

Remediation

Set the minimum protocol to TLS 1.2 (tls.VersionTLS12, ssl.TLSVersion.TLSv1_2, SSLContext.getInstance("TLS") with setEnabledProtocols(new String[]{"TLSv1.3", "TLSv1.2"})).
Offer only AEAD cipher suites (AES-GCM, ChaCha20-Poly1305) with forward secrecy, or leave the library defaults in place.
Keep SSLv3, TLSv1 and TLSv1.1 in jdk.tls.disabledAlgorithms.

References

Suppressing this rule

Put a nosec comment on the line, or on line 1 to cover the whole file. Use the comment marker of the file’s language (#, //, -- or ;):

# nosec vnx-757
// nosec vnx-757

Or record an ignore rule: vulnetix ignore add --rule vnx-757 --reason "...". See Suppressing findings.